2013
12-04

# Children’s Queue

There are many students in PHT School. One day, the headmaster whose name is PigHeader wanted all students stand in a line. He prescribed that girl can not be in single. In other words, either no girl in the queue or more than one girl stands side by side. The case n=4 (n is the number of children) is like
FFFF, FFFM, MFFF, FFMM, MFFM, MMFF, MMMM
Here F stands for a girl and M stands for a boy. The total number of queue satisfied the headmaster’s needs is 7. Can you make a program to find the total number of queue with n children?

There are multiple cases in this problem and ended by the EOF. In each case, there is only one integer n means the number of children (1<=n<=1000)

For each test case, there is only one integer means the number of queue satisfied the headmaster’s needs.

1
2
3

1
2
4

a.男孩，任何n – 1的合法队列追加1个男孩必然是合法的，情况数为f[n - 1]；
b.女孩，在前n – 1的以女孩为末尾的队列后追加1位女孩也是合法的，我们可以转化为n – 2的队列中追加2位女孩；
一种情况是在n – 2的合法队列中追加2位女孩，情况数为f[n - 2]；

但我们注意到本题的难点，可能前n – 2位以女孩为末尾的不合法队列（即单纯以1位女孩结尾），也可以追加2位女孩成为合法队列，而这种n – 2不合法队列必然是由n – 4合法队列+1男孩+1女孩的结构，即情况数为f[n - 4]。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cmath>
using namespace std;
const int mod = 100000;
int a[1003][50];
int main()
{
int n,i,j;
a[1][1] = 1;
a[2][1] = 2;
a[3][1] = 4;
a[4][1] = 7;
for(i = 5; i <= 1000; i ++)
{
for(j = 1; j < 50; j ++)
{
a[i][j] += a[i-1][j] + a[i-2][j] + a[i-4][j];
a[i][j+1] += a[i][j]/mod;
a[i][j] %= mod;
}
}
while(~scanf("%d",&n))
{
j = 49;
while(!a[n][j])
j--;
printf("%d",a[n][j]);
for(--j; j >=1; j--)
printf("%05d",a[n][j]);
printf("\n");
}
return 0;
}

1. 嗯 分析得很到位，确实用模板编程能让面试官对你的印象更好。在设置辅助栈的时候可以这样：push时，比较要push的elem和辅助栈的栈顶，elem<=min.top()，则min.push(elem).否则只要push（elem）就好。在pop的时候，比较stack.top()与min.top(),if(stack.top()<=min.top()),则{stack.pop();min.pop();}，否则{stack.pop();}.

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